Urinary tract infections (UTI) are the most common bacterial infection in the developed world and uropathogenic E. coli (UPEC) account for greater than 80% or these infections. One of the strongest risk factors for the development of frequent recurrent (rUTI), which occurs in 2-7% of women, is a family history of rUTI, suggesting a genetic component to UTI susceptibility. This conclusion is further supported by mouse models of UTI, which demonstrate high levels of strain to strain variation in mouse susceptibility to UTI. An in silico whole genome analysis of single nucleotide polymorphisms (SNPs) conserved in UTI susceptible mouse strains and excluded from UTI resistant mouse strains identified several non-synonymous SNPs in the protein coding portion of the innate immune receptor toll-like receptor 1 (TLR1), as well as a SNP predicted to disrupt a splice site in this gene. The TLR1 protein is a pattern recognition receptor that complexes with TLR2 to detect bacterial lipoproteins and activate the immune system in response to this stimulus. Preliminary results suggest that macrophages from the UTI susceptible mouse strain C3H/HeN are dramatically less responsive to the TLR1 specific agonist Pam3cys than macrophages from the UTI resistant mouse strain C57Bl/6. In addition, gene expression of Tlr1 is reduced in the susceptible strain relative to the resistant strain. The goal of this study is to examine the role of TLR1 in UTI and o determine how polymorphisms in the Tlr1 gene influence susceptibility to UTI. This will be accomplished by examining the UTI susceptibility in C56Bl/6 Tlr1 -/- mice and other strains with various Tlr1 polymorphisms. These studies will be followed by an examination of the effects of genetic variation on the expression, translation, protein trafficking and signaling of TLR1 in vitr, using tissue culture based expression and functional analysis. In vivo, the effect of Tlr1 genetic variation on UTI susceptibility in different mouse genomic backgrounds will be assessed by examining other mouse strains with altered Tlr1 gene sequences or by introducing specific alleles via targeted breeding. Genomic background effects and the role of TLR1 function on bone marrow derived immune cells in influencing UTI susceptibility will be elucidated by generating mouse bone marrow chimeras and assessing their sensitivity to UTI. Finally, the existence of a correlation between Tlr1 variation and UTI susceptibility in the human population will be examined by sequencing the Tlr1 locus of 250 individuals with frequent rUTI and comparing these sequences to general databases of human genome sequences and to a control population not prone to rUTI. This analysis will provide evidence for the use of Tlr1 sequences from patients to determine their propensity to UTI. Understanding the role of TLR1 and its polymorphisms in UTI susceptibility will allow for a better understanding of the pathogenesis of UTI as well as targeted therapies and predictive outcomes for individuals afflicted with rUTI.